Question: On the first 3 quizzes of his language class, Christopher got an average score of 82. What does he need on the next quiz to have an overall average of 84?
Let his score on the next quiz be $x$ The sum of all of his scores is then $3 \cdot 82 + x$ The same sum must also be equal to $4 \cdot 84$ Solve: $x = 4 \cdot 84 - 3 \cdot 82 = 90$.